222 BOTANY AND PHARMACOGNOSY. 



all the energy formed is used by the plantlet, much of it escaping 

 as heat, as in the germination of barley in the preparation of malt 

 (p. 575). Those plants dependent upon the presence of free 

 atmospheric oxygen are called aerobes^ while those which are 

 not thus dependent, as certain fungi and bacteria, are called 



ANAEROBES. 



Metabolism. Processes of construction and destruction are 

 going on simultaneously in the plant, and these are all grouped 

 under the general name of metabolism. The processes whereby 

 complex substances are built up from simpler ones, as in photo- 

 synthesis, are together spoken of as constructive aietabolism 

 (anabolism), while those which involve the breaking down of 

 complex compounds into simpler ones, either through oxidation 

 or other chemical action, as when sugar is changed into carbon 

 dioxide and water, are grouped under the head of destructive 

 metabolism (catabolism). 



Inasmuch as the carbon dioxide of the atmosphere and the 

 water taken up by the roots together with the mineral salts which 

 it hcjlds in solution are the only sources of the food supply of 

 green plants, it follows that the highly complex proteins trace 

 their origin to these comparatively simple substances. By some 

 it is supposed that the final stages in the building up or synthesis 

 of the proteins take place in the leaves, but it is probable that they 

 take place in all the growing parts of the plant. It has already 

 been stated in the paragraph on proteins that seeds contain re- 

 serve materials which are broken up into simpler compounds 

 through the action of certain enzymes, and thus made available 

 for the seedling. It is claimed that these compounds are prin- 

 cipally amino acids, and that of these aspartic and glutaminic acids 

 occur in largest amount and that these two acids are found in 

 dififerent relative amounts in different plants. It is furthermore 

 claimed by some authors that by certain syntheses these com- 

 pounds are respectively converted into asparagin and glutamin. 

 both of which occur as reserve materials in seeds and in other 

 parts of plants as well. Yet other syntheses take place whereby 

 asparagin and similar bodies arc converted into albun.iin and other 

 proteins. In the Coniferae the part played by asparagin and 

 glutamin in protein syntheses is taken by arginin. which substance 

 is found in considerable amouui in the seeds of the plants of this 

 group. 



